In addition to lack of support for switching between GPU chipsets, the presence of Optimus can actually prevent the use of Nvidia chipset, even if installed GPU drivers support it.[3] Some older systems contain a hardware switch (mux) to switch the output between the two video devices, which could be set in the BIOS. Modern systems lack the hardware muxer and output is often hardwired to integrated chipset's display controller. With Optimus, the output frames from the Nvidia card are therefore transferred over the PCIe bus to the integrated chipset's framebuffer, which is then displayed. This transfer is not working using official driver on anything except Windows 7 because of lacking architectural infrastructure of other operating systems.

The open-source project Bumblebee tries to support these kinds of graphics cards.

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It seems as people have a hard time getting the card to work, compared to the slower onboard which is probably whats causing the "slowness".